Within the recent developments on the field of the Internet Protocol (IP) Multimedia Subsystem (IMS), it is expected that many types of application servers (AS) are connected to the IMS System. One example thereof is an application server for the Push-to-talk-over-Cellular (PoC) service, which is also known as Push-To-Talk (PTT) service. With the PoC-service, a subscriber can be connected to a number of other subscribers, which are pre-selected by himself/herself by simply pressing a key on the user equipment (UE). This establishes a GPRS-connection, which operates in half-duplex mode. The PoC-service is considered to be one of the first implemented VoIP-applications.
The capabilities of the application server are provided by the IMS. These capabilities can be utilized to implement services for the subscribers and include, for example, the registration of a third party from the IMS towards the application server.
However, if every subscriber maintains one or more real-time Packet Data Protocol (PDP) contexts at the same time, this would bind a lot of expensive packet core and radio resources.